Pathobiology of Cancer
Cancer is characterized primarily by an increase in the number of abnormal cells derived from a given normal tissue, invasion of adjacent tissues by these abnormal cells, or lymphatic or blood-borne spread of malignant cells to regional lymph nodes and to distant sites. Clinical data and molecular biologic studies indicate that cancer is a multistep process that begins with minor preneoplastic changes, which may under certain conditions progress to neoplasia. The neoplastic lesion may evolve clonally and develop an increasing capacity for invasion, growth, metastasis, and heterogeneity, especially under conditions in which the neoplastic cells escape the host's immune surveillance. (Roitt, I., Brostoff, J. and Kale, D., Immunology, 17.1-17.12 (3rd ed., Mosby, St. Louis, Mo., 1993))
Various stages of tumor development can be described generally as follows:
a) Tumor evolution commences when a cell within a normal population sustains a genetic mutation that expands its tendency to proliferate.
b) Such genetically altered cells and their offspring continue to appear normal, but they reproduce excessively and lead to a condition termed hyperplasia. The altered cells may also secrete signaling factors or other molecules that cause changes in their local cellular and extracellular environment, including without limitation, the response of the immune system to them. Such environmental effects may in turn affect the viability, proliferation, and further mutations of the altered cells. After some time (months or years) a very small fraction of these altered cells may sustain additional mutation with subsequent loss of control of cell growth and further potential effects on their environment.
c) The offspring of these cells not only proliferate excessively but also appear abnormal in shape and in orientation. The tissue is now said to exhibit a condition termed dysplasia. After some time, one or more additional mutations may further alter cell behavior and the effect of the cells on their environment.
d) The influenced and genetically altered cells turn still more abnormal in growth and appearance. If the tumor mass does not invade through any boundaries between tissues, it is termed an in situ tumor. This tumor may stay contained indefinitely, however, some cells may acquire still more mutations.
e) A malignant or invasive tumor results if the genetic changes allow the tumor mass to initiate invading underlying tissue and to cast off cells into the blood or lymph. The defector cells may install new tumors loci (metastases) throughout the body.
Metastases represent the end products of a multistep cell-biological process termed the invasion-metastasis cascade, which involves dissemination of cancer cells to anatomically distant organ sites and their subsequent adaptation to foreign tissue microenvironments. Each of these events is driven by the acquisition of genetic and/or epigenetic alterations within tumor cells and the co-option of non-neoplastic stromal cells, which together endow incipient metastatic cells with traits needed to generate macroscopic metastases. (Volastyan, S., et al., Cell, 2011, vol. 147, 275-292)
An enormous variety of cancers affect different tissues throughout the body, which are described in detail in the medical literature. Over 85% of human cancers are solid tumors, including carcinomas, sarcomas and lymphomas. Different types of solid tumors are named for the type of cells that form them. Examples include cancer of the lung, colon, rectum, pancreatic, prostate, breast, brain, and intestine. Other human tumors derive from cells involved in the formation of immune cells and other blood cells, including leukemias and myelomas.
The incidence of cancer continues to climb as the general population ages, as new cancers develop, and as susceptible populations grow. A tremendous demand therefore exists for new methods and compositions that can be used to treat subjects with cancer.
Methods of Treating Cancer
Current cancer therapy may involve surgery, chemotherapy, hormonal therapy, biological therapy, targeted therapy, immunotherapy and/or radiation treatment to eradicate neoplastic cells in a patient (see, e.g., Stockdale, 1998, Medicine, vol. 3, Rubenstein and Federman, eds., Chapter 12, Section IV; and Baudino TA “Targeted Cancer Therapy: The Next Generation of Cancer Treatment”, Curr Drug Discov Technol. 2015; 12(1):3-20).
Such therapies may be used independently or in combinations. Choices of therapy will depend on the history and nature of the cancer, the condition of the patient, and, under the circumstances, the anticipated efficacy and adverse effects of the therapeutic agents and methods considered.
With respect to chemotherapy, there are a variety of chemotherapeutic agents and methods of delivery of such agents available for the treatment of different cancers. Most first generation chemotherapeutic agents were not tumor specific, have broad systemic effects, are toxic, and may cause significant and often dangerous side effects, including severe nausea, bone marrow depression, and immunosuppression.
Additionally, even with administration of combinations of chemotherapeutic agents, many tumor cells are or become resistant to chemotherapeutic agents. In fact, cells resistant to the particular chemotherapeutic agents used in a treatment protocol often prove to be resistant to other drugs, even if those agents act by different mechanism from those of the drugs used in the specific treatment. This phenomenon is referred to as multidrug resistance. Because of drug resistance, many cancers prove refractory to standard chemotherapeutic treatment protocols.
Thus, there exists a significant need for alternative compounds, compositions and methods for treating, preventing and managing cancer.
Further, whereas surgical resection and adjuvant therapy can cure well-confined primary tumors, metastatic disease is largely incurable because of its systemic nature and the resistance of disseminated tumor cells to existing therapeutic agents. This explains why greater than 90% of mortality from cancer is attributable to metastases, not the primary tumors from which these malignant lesions arise.
Pathobiology of Inflammatory Disease
Inflammation is a complex protective biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, involving immune cells, blood vessels, and molecular mediators. The function of inflammation is to eliminate the initial cause of cell injury, clear out necrotic cells and tissues damaged from the original insult and the inflammatory process, and to initiate tissue repair. (Ferrero-Miliani L, Nielsen OH, Andersen PS, Girardin SE; Nielsen; Andersen; Girardin (February 2007) Clin. Exp. Immunol. 147)
Inflammation is classified as either acute or chronic. Acute inflammation is the initial response of the body to harmful stimuli and is achieved by the increased movement of plasma and leukocytes (especially granulocytes) from the blood into the injured tissues. A series of biochemical events propagates and matures the inflammatory response, involving the local vascular system, the immune system, and various cells within the injured tissue.
Prolonged inflammation, known as chronic inflammation, is characterized by simultaneous destruction and healing of the tissue from the inflammatory process. It leads to a progressive shift in the type of cells present at the site of inflammation, such as mononuclear cells, and increases in systemic concentrations of cytokines such as TNF-α, IL-6, and CRP. (Petersen, A. M.; Pedersen, B. K. (2005). J Appl Physiol. 98 (4): 1154-1162)
Many proteins are involved in inflammation. Any of them are susceptible to genetic mutation which may impair or otherwise dysregulate their normal function and expression.
Methods of Treating Inflammatory Disease
Both small molecules and biologics are used to treat inflammatory diseases. Most treatments, however, are largely palliative.
A clear unmet medical need remains to find treatments that can mechanistically reduce chronic inflammatory diseases.
Pathobiology of Fibrotic Disease
Fibrosis, or the accumulation of extracellular matrix molecules that constitute scar tissue, is a common result of tissue injury. Pulmonary fibrosis, renal fibrosis, and hepatic cirrhosis are among the common fibrotic diseases which altogether represent a large unmet medical need. (Friedman SL, Sheppard D, Duffield JS, Violette S. Sci Transl Med Jan9;5(167)
Mechanisms of fibrogenesis include inflammatory as well as other pathways and generally involve reorganization of the actin cytoskeleton of affected cells, including epithelial cells, fibroblasts, endothelial cells, and macrophages.
Actin filament assembly and actomyosin contraction are directed by the Rho-associated coiled-coil forming protein kinase (ROCK) family of serine/threonine kinases (ROCK1 and ROCK2) and thus Rho is associated with fibrogenesis.
Tissue fibrosis is a leading cause of morbidity and mortality. 45% of deaths in the United States are attributable to fibrotic disorders. (Wynn TA. “Fibrotic Disease and the TH1/TH2 Paradigm.” Nat Rev Immunol 2004 August: 4(8): 583-594.) Treatments are generally palliative.
Idiopathic pulmonary fibrosis (IPF) is characterized by progressive lung scarring, short median survival, and limited therapeutic options, creating great need for new pharmacologic therapies. It is thought to result from repetitive environmental injury to the lung epithelium.
Targeted Therapy of Cancer, Inflammatory, and Fibrotic Diseases
Targeted therapies are a cornerstone of what is also referred to as precision medicine, a form of medicine that uses information about a person's genes and proteins to prevent, diagnose, and treat disease. Such therapeutics are sometimes called “molecularly targeted drugs,” “molecularly targeted therapies,” or similar names. The process of discovering them is often referred to as “rational drug design.”
A series of actions among molecules in a cell that leads to a certain end point or cell function is referred to as a molecular pathway.
Molecularly targeted drugs interact with a particular target molecule, or structurally related set of target molecules, in a pathway; thus modulating the endpoint effect of that pathway, such as a disease-related process; and, thus, yielding a therapeutic benefit.
Molecularly targeted drugs may be small molecules or biologics, usually antibodies. They may be useful alone or in combinations with other therapeutic agents and methods.
Because they target a particular molecule, or related set of molecules, and are usually designed to minimize their interactions with other molecules, targeted therapeutics may have fewer adverse side effects.
Targeted cancer drugs block the growth and spread of cancer by interacting with specific molecules or sets of structurally related molecules (altogether, “molecular targets”) that are involved, broadly speaking, in the growth, progression, lack of suppression or elimination, or spread of cancer. Such molecular targets may include proteins or genes involved in one or more cellular functions including, for example and without limitation, signal transduction, gene expression modulation, apoptosis induction or suppression, angiogenesis inhibition, or immune system modulation.
In some cases, the development of targeted cancer therapeutics involves identifying genes or proteins that are present in cancer cells but not normal cells or that are more abundant or more highly stimulated in cancer cells, especially if they are known to be involved in cancer processes, and then discovering agents that will interact with those targets and be associated with a desired therapeutic effect.
Targeted cancer therapies generally differ from standard cancer chemotherapy in several ways:                a. Targeted therapies are deliberately chosen or designed to interact with their target(s), whereas many standard chemotherapies were identified because they were found in general to kill cells.        b. Targeted therapies are intended to act on specific molecular targets that are associated with cancer, whereas most standard chemotherapies act on all rapidly dividing normal and cancerous cells. They may, however, also have known and sometime unknown interactions with other molecules, so-called off-target effects.        c. Most targeted therapies are cytostatic (that is, they block tumor cell proliferation), whereas standard chemotherapy agents are usually cytotoxic (that is, they kill tumor cells). However, some targeted therapies such as Antibody Drug Conjugates are cytotoxic.        
Targeted therapy monoclonal antibodies (mAbs) and targeted small molecules are being used as treatments for inflammatory diseases (Kotsovilis S, Andreakos E., Methods Mol Biol. 2014;1060:37-59). They are used either as a monotherapy or in combination with other conventional therapeutic modalities, particularly if the disease under treatment is refractory to therapy using solely conventional techniques.
Some treatments for fibrotic disorders, such as idiopathic pulmonary fibrosis, hepatic fibrosis, and systemic sclerosis, target inflammatory pathways.
The Ras GTPase Family
The Ras superfamily of proteins are small GTPases with substantial amino acid sequence homology that act as signal transducers between cell surface receptors and several intracellular signaling cascades. These molecules are involved in the regulation of such essential cellular functions as cell survival, proliferation, motility, and cytoskeletal organization (see Karnoub et al., Nat. Rev. Mol. Cell Biol., 9: 517-531 (2008)).
Research has defined a number of subfamilies of the Ras superfamily, based largely on amino acid sequence homologies. These subfamilies are often referred to in an abbreviated manner based on the most commonly studied member of the class.
The GTP binding domains of one subfamily of the Ras superfamily having substantial sequence homology is commonly referred to as the Ras family or Ras.
There are four isoforms of Ras proteins, expressed from three different genes: H-Ras (Harvey sarcoma viral oncogene), N-Ras (neuroblastoma oncogene), and the splice variants K-Ras4A and K-Ras4B (Kirsten sarcoma viral oncogene) (see Karnoub et al., supra).
The GTP binding domains of another subfamily of the Ras superfamily having substantial sequence homology, is commonly referred to as the Rho family and includes proteins and groups of proteins referred to as Rho, Rac and Cdc42.
Ras Function and Pathways
All Ras isoforms share sequence identity in all of the regions that are responsible for GDP/GTP binding, GTPase activity, and effector interactions, suggesting a functional redundancy. However, studies clearly demonstrate that each Ras isoform functions in a unique, different way from the other Ras proteins in normal physiological processes as well as in pathogenesis (Quinlan et al., Future Oncol., 5: 105-116 (2009)).
Ras proteins cycle between ‘on’ and ‘off’ conformations that are conferred by the binding of GTP and GDP, respectively. Under physiological conditions, the transition between these two states is regulated by guanine nucleotide exchange factors (GEFs), which promote the activation of Ras proteins by stimulating the exchange of GDP for GTP exchange, and by GTPase-activating proteins (GAPs), which accelerate Ras-mediated GTP hydrolysis to GDP.
Several cell surface receptors activate Ras, such as Receptor Tyrosine Kinases (RTKs), growth factor receptors, cytokine receptors and integrins.
Once activated, Ras initiates signaling of the “MAPK pathway” (also referred to as the Ras-RAF-MEK-MAPK/ERK pathway) that affects cell growth, differentiation, proliferation, apoptosis and migration. It is also associated with other molecular pathways including phosphoinositide 3-kinases (PI3Ks), Rac1 GEF, and the Ra1-guanine nucleotide dissociation stimulator (GDS).
The MAPK pathway operates through a sequence of interactions among kinases. Activated by Ras in the “on”, GTP bound, state, a MAPK kinase kinase (MAPK3), such as Raf, MLK, or TAK, phosphorylates and activates a MAPK kinase, such as MEK, which then phosphorylates and increases the activity of one or more MAPKs, such as ERK1/2. PI3K is part of the PI3K/AKT/mTOR pathway regulating intracellular signaling important for several cellular functions such as survival, anti-apoptotic and cell cycle.
Ras Dysfunction Is Causally Associated with Important Diseases and Disease Processes
Ras and its downstream pathways, including MAPK, have been studied extensively. They are causally associated with a range of diseases, including certain cancers, inflammatory disorders, Ras-associated autoimmune leukoproliferative disorder, and certain Rasopathies.
There is more than one distinct route to aberrant Ras activation including mutational activation of Ras itself, excessive activation of the wild-type protein through upstream signaling, and loss of a GAP function that is required to terminate activity of the protein.
One million deaths per year are attributed in the literature to mutations in K-Ras alone. (Frank McCormick. “K-Ras protein as a drug target.” Journal of Molecular Medicine (Berlin) 2016: 94: 253-258)
Ras is well documented in the literature as an oncogene. Ras oncogenes can initiate cancer in model organisms. Microinjection studies with antibodies that block Ras activity or block specific mutant alleles of Ras; ablation of K-Ras in mouse models of lung adenocarcinoma or pancreas cancer; and ablation of H-Ras all lead to tumor regression in mouse models.
About 30% (Prior IA, Lewis PD, Mattos C. Cancer Res. 2012 May 15;72(10):2457-67) of human cancers have a mutated Ras protein with the most frequent mutations in residues G12, G13 and Q61. These oncogenic mutations result in impaired GTP hydrolysis and accumulation of Ras in the GTP-bound state leading to increased activation of Ras-dependent downstream effector pathways.
Table 1 summarizes recent data concerning the frequency of K-Ras and N-Ras mutations in an illustrative, but not exhaustive list, of human malignancies.
TABLE 1MutationTumor TypeFrequencyK-RasPancreas71%K-RasColon35%K-RasSmall intestine35%K-RasBiliary tract28%K-RasEndometrium22%K-RasLung20%N-RasSkin (melanoma)20%K-RasCervix19%K-RasUrinary tract16%Stephen A G, Esposito D, Bagni R K, McCormick F. Cancer Cell. 2014 Mar. 17; 25(3): 272-81.
Ras mutants, and in some cases Ras over-activation, are associated in the literature with a wide range of significant cancer associated processes including: cell proliferation, DNA checkpoint integrity, replicative stress related clonal selection, suppression of apoptosis, metabolic reprogramming, autophagy, microenvironment remodeling, immune response evasion, and metastatic processes. The detailed mechanisms, interdependencies, and frequency of these effects across different tumor types and stages of cancer development remain to be elucidated comprehensively.
Proliferative effects associated in the literature with oncogenic Ras include transcriptional upregulation of growth factors; upregulation of growth factor receptor expression; upregulation of integrins that promote proliferation and downregulation of those associated with cellular quiescence; upregulation of transcription factors required for cell cycle entry; acceleration through cell cycle transitions; downregulation of anti-proliferative TGFβ signaling; and the suppression of cyclin-dependent kinase inhibitors.
MAPK signaling has been shown to enhance programmed death-ligand 1 (PD-L1) expression in KRas mutant lung cancer cells and thus Ras mutations are associated with the suppression of immune responses to cancer. (Sumimoto et al., PLOS One 2016 Nov. 15; DOI: 10.1371/journal.pone.0166626) Anti-PD-1 and anti-PD-L1 monoclonal antibodies have demonstrated clinical activity against tumors including non-small cell lung cancers.
Ras is also implicated through the MAPK pathways as a cause of a range of pathological inflammatory conditions. In addition to ERK1/2, the MAPKs ERK5, c-Jun N-terminal kinases (JNKs) and p38 isoforms have been shown to be implicated in inflammatory response. (Huang, et al. 2010, Protein Cell, 1(3), 218-226)
Ras is causally associated with inflammatory diseases including the following: rheumatoid arthritis (Abreu JR, de Launay D, Sanders ME, Grabiec AM, Sande van de MG, Tak PP, Reedquist KA: The Ras guanine nucleotide exchange factor RasGRF1 promotes matrix metalloproteinase-3 production in rheumatoid arthritis synovial tissue. Arthritis Res Ther. 2009, 11: R121-10.1186/ar2785), which is the most common cause of disability (Hootman JM, Brault MW, Helmick CG, Theis KA, Armour BS. Prevalence and most common causes of disability among adults—United States 2005, MMWR, 2009, 58(16):421-6); atherosclerosis (Fonarow G (2003), Cleve. Clin. J. Med. 70: 431-434); inflammatory bowel disease (IBD), such as Crohn's disease (Ignacio CS, Sandvik AK, Bruland T, Andreu-Ballester JC, J. Crohns Colitis, 2017 Mar. 16. doi: 10); ulcerative colitis, spondyloarthropathies, idiopathic pulmonary fibrosis, juvenile arthritis, psoriasis, psoriatic arthritis, and others.
Ras has been causally associated with Ras-associated autoimmune leukoproliferative disorder, a nonmalignant clinical syndrome initially identified in a subset of putative autoimmune lymphoproliferative syndrome (ALPS) patients. (Katherin Calvo, et al. “JMML and RALD (Ras-associated autoimmune leukoproliferative disorder): common genetic etiology yet clinically distinct entities” Blood, 2015 Apr. 30; 125(18): 2753-2758)
Aberrant Ras signaling is causally implicated in the family of Rasopathies including neurofibromatosis type 1, Noonan's syndrome, and Costello syndrome.
Ras as a Therapeutic Molecular Target
Interference with Ras superfamily member signaling in cell based and animal models of the aforementioned diseases modulates disease processes.
Ras superfamily proteins, and particularly Ras and downstream pathway elements, have thus long been discussed as theoretical molecular targets for the development of targeted therapeutics. In theory, a molecule could serve as a therapeutic agent in diseases associated with aberrant Ras signaling if it could disrupt such Ras signaling.
In theory, it was recognized that a mechanism for downregulating aberrant Ras signaling could be to interfere with one or more steps in the Ras signaling process involving GTP binding in a manner that left the Ras in other than an “on” configuration. However, while this was a concept in theory, based on two widely accepted findings, it has also long been accepted by the scientific community that it would not be possible to achieve.
GTP and GDP had been found to bind to the GTP binding domain of Ras with single to double digit picomolar affinities.
The cellular concentration of GTP had been found to be substantially in excess of this range.
The widely accepted findings concerning the single to double digit picomolar range of affinities of GTP and GDP for the Ras GTP binding domain were determined by kinetic and filter binding measurements between Ras and radiolabeled GDP and GTP (Feuerstein J, Kalbitzer HR, John J, Goody RS, Wittinghofer A. Eur. J. Biochem., 1987 Jan. 2, 162(1):49-55; and John J, Sohmen R, Feuerstein J, Linke R, Wittinghofer A, Goody RS. Biochemistry, 1990 Jun. 26, 29(25):6058-65).
Consistent with these findings, and often citing them, the GTP binding domain of Ras has widely been accepted and reported in preeminent journal editorials, reviews, and research papers to be “undruggable.” (Papke B, Der CJ., Science, 2017 Mar. 17, 355(6330):1158-1163; Stephen AG, Esposito D, Bagni RK, McCormick F, Cancer Cell, 2014 Mar. 17, 25(3):272-81; and Ostrem JM, Shokat KM, Nat. Rev. Drug Discov., 2016 Nov., 15(11):771-785)
Accordingly, research concerning targeted Ras therapeutics has focused on domains of the Ras protein other than the GTP binding site. These include, for example, farnesyltransferase inhibitors (FTIs) that prevent Ras attachment to the inner side of the plasma membrane, and molecules that compete with the interaction of Ras with the exchange factor SOS or downstream effectors.
Thus, it has been thought that a molecule could not be developed to compete with GTP binding to the GTP binding domain of Ras. Compounds that do so, however, would fill a need in the field.
The Rho Family Function and Pathways
The Rho subfamily of the Ras superfamily currently includes approximately 22 proteins most of which scientists commonly divide into subgroups including those referred to as Cdc42, Rac, and Rho. (Boureux A, Vignal E, Faure S, Fort P (2007).“Evolution of the Rho family of ras-like GTPases in eukaryotes”. Mol Biol Evol 24 (1): 203-16).
The three most commonly studied members of the Rho subfamily have been Cdc42, Rac1, and RhoA.
The Cdc42 group includes Cdc42, TC10, TCL, Chip, and Wrch-1.
The Rac group includes Rac1, Rac2, Rac3, and RhoG.
The RhoA group includes RhoA, RhoB, and RhoC.
Other Rho subfamily GTPases not included in the Cdc42, Rac, or Rho groups include RhoE/Rnd3, RhoH/TTF, Rif, RhoBTB1, RhoBTB2, Miro-1, Miro-2, RhoD, Rnd1, and Rnd2.
Like other Ras superfamily proteins, the Rho subfamily GTPases cycle between ‘on’ and ‘off’ conformations that are conferred by the binding of GTP and GDP, respectively. Under physiological conditions, the transition between these two states is regulated by guanine nucleotide exchange factors (GEFs), which promote the activation of Rho subfamily proteins by stimulating the release of GDP and the binding of GTP, and by GTPase-activating proteins (GAPs), which accelerate Rho subfamily member-mediated GTP hydrolysis to GDP. Guanine nucleotide dissociation inhibitors (GDIs) proteins form a large complex with the Rho protein, helping to prevent diffusion within the membrane and into the cytosol and thus acting as an anchor and allowing tight spatial control of Rho activation.
The Rho subfamily members are intracellular proteins that affect a large number of downstream pathways broadly involving cytoskeleton organization, cell polarity, migration, transcription and proliferation, and, more particularly, membrane and vesicular trafficking, cell cycling, microtubule stability, actin membrane linkages, actin polymerization, myosin phosphorylation, API dependent gene expression, cell adhesion, cell contractility, cell adhesion, and MTOC orientation. (Martin Schwartz. “Rho Signalling at a Glance.” Journal of Cell Science. 2004: (117:pp. 5457-5458).and (Bustelo XR, Sauzeau V, Berenjeno IM (2007). “GTP-binding proteins of the Rho/Rac family: regulation, effectors and functions in vivo” BioEssays. 29 (4): 356-370).
Rho Family Dysfunction Is Causally Associated with Important Diseases
Rho subfamily GTPases have been reported to contribute to most steps of cancer initiation and progression including the acquisition of unlimited proliferation potential, survival and evasion from apoptosis, angiogenesis, tissue invasion, motility, and the establishment of metastases. (Matteo Parri and Paolo Chiarugi. “Rac and Rho GTPases in Cancer Cell Motility Control.” Cell Communication and Signalling. 2010(8:23))
High Rho subfamily protein levels are frequently associated with human tumors. High RhoA levels have been associated with human liver, skin, colon, ovarian, bladder, gastric, esophageal squamous cell, testicular, and breast cancer. High Rho B, C, or H levels have been associated with breast, squamous cell, pancreatic, breast, liver, ovarian, head and neck, prostate, non-small cell lung, and gastric cancers and melanoma metastase. High Rac1 levels have been associated with human testicular, gastric, breast, and squamous cell cancers. High Rac2 or Rac3 have been associated with breast colon, head and neck, and squamous cell cancers. (Matteo Parri and Paolo Chiarugi. “Rac and Rho GTPases in Cancer Cell Motility Control.” Cell Communication and Signalling. 2010(8:23). Gain-of-function mutations such as P29S of Rac1 were detected in melanoma, breast, head and neck cancers (Alan JK, Lundquist EA. Mutationally activated Rho GTPases in cancer. Small GTPases. 2013 Jul.-Sep.;4(3):159-63)
Unlike Ras proteins, which are frequently mutated in cancer (around 30%), Rho subfamily proteins themselves are generally not found to be mutated in cancer. Rather, aberrant activity of Rho subfamily proteins in cancer appears to occur by overexpression of these proteins or by aberrant regulation of molecules that control their activity, such as activation or overexpression of GEFs and inactivation or loss of GAPs or GDIs (Alan JK, Lundquist EA. Mutationally activated Rho GTPases in cancer. Small GTPases. 2013 Jul.-Sep.;4(3):159-63).
Interactions between Rac and Rho proteins are believed to modulate certain forms of mesenchymal and amoeboid cell movement associated with cancer.
Rho subfamily associated kinases (ROCK1 and ROCK2) are implicated as mediators of multiple profibrotic processes including those associated with idiopathic pulmonary fibrosis. (Knipe RS, Tager EM, and Liao JK. “The Rho kinases: critical mediators of multiple profibrotic processes and rational targets for new therapies for pulmonary fibrosis.” Pharmacol Rev. 2015 67(1):103-17.)
Rho family members as Therapeutic Molecular Targets
Given their roles in disease processes, Rho subfamily members have been identified as potential Therapeutic Molecular Targets.
Rho subfamily members have been identified as potential Therapeutic Molecular Targets in cancer.
Rho subfamily members have been identified as potential Therapeutic Molecular Targets in fibrotic disease.